First-principles modelling of WTe2 and graphene/WTe2 bilayer heterostructures

In this dissertation, the structural, electronic, topological and spin-related properties of monolayer WTe2 and WTe2/graphene bilayer heterostructures are investigated theoretically. Monolayer WTe2 is a layered transition metal dichalcogenide with a distinctive highly anisotropic atomic structure which was recently confirmed as a quantum spin Hall material. It was further shown to display gate-tunable low-density superconductivity as well as non-trivial geometric properties and is predicted to feature high spin-orbit coupling and non-trivial spin-textures. The interplay between these outstanding properties might be of great interests in various fields such as quantum computation, spintronics or dissipationless electronic devices. A natural question is whether one can transfer these properties to other layered materials by forming Van der Waals heterostructures. In particular, WTe2/graphene bilayers offer the prospect of proximity-induced spin-orbit coupling in graphene. This could effectively lead to non-trivial spin-textures and topological phases in this material, which would offer great perspectives for the integration of graphene in spin-based electronics. In particular, this thesis sheds light on the most stable structural phase adopted by monolayer WTe2 in free-standing conditions. It further predicts a giant spin-orbit proximity effect in graphene, which displays sizable anisotropy and largely preserves the linear semimetallic behaviour. Moreover, computations reveal the presence of an electric dipole moment in the bilayer heterostructure, which should affect spin-textures in the structure and provide a way to control them via electric means. Although these findings certainly require further confirmation, this investigation also potentially suggests that monolayer WTe2 induces a canted spin-texture in the conduction bands of the Dirac cone as well as a topological phase in graphene.